The gastrointestinal (GI) tract is exposed to environmental agents from ingested food, food additives, and the pollutants that escape the lung defense systems. In the GI tract, membranous epithelial cells (mast cells) transport environmental agents or antigens to the underlying lymphoid follicles or Peyer's patches. For the development of the response, antigens must come in contact with lymphocytes and macrophages present in Peyer's patches. In bowel from normal subjects and patients with a variety of diseases, the presence of antigenic inorganic particles from the environment have been found in macrophages located in the deep aspect of Peyer's patches. The overall hypothesis of this study is that the interactions between environmental agents and "GI immune cells" such as mast cells or macrophages of Peyer's patches are oxidative, involving free radical formation. Three Specific Aims will be tested. Specific Aim #1 is to determine superoxide and sulfur trioxide radical production (using electron paramagnetic resonance spin trapping technique) and hydrogen peroxide release (using cell-permeant dichlorodihydrofluorescein diacetate probe): (a) in vitro after addition of sulfites to "GI immune cells" and (b) ex vivo using "GI immune cells" isolated from rats treated with a stimulator of inflammatory response endotoxin. Synergy on free radical production between sulfites and endotoxin will be determined. Specific Aim #2 is to measure hydroxyl radical adduct formation using EPR spin trapping of "GI immune cells" exposed to titanium oxide or silicates in the presence of the biological reductant ascorbic acid. Similar in vitro and ex vivo experiments (with titanium oxide or silicates replacing the bisulfites) will be carried out as outlined in Specific Aim #1. Specific Aim #3 is to establish co- culture systems consisting of mast cells or isolated "GI immune cells" and intestinal epithelial cells (cell line, IEC-6) and to characterize oxidative biomarkers as well as transepithelial electrical resistance of IEC-6 cells after an addition of sulfites, titanium oxide, or silicates to mast cells or isolated "GI immune cells". This research program is designed to investigate basic mechanisms of oxidative activities due to exposure of bisulfites, titanium oxide and silicas to GI immune cells, and the predisposition of hosts to exacerbated injury when experiencing systematic inflammatory infection. The relevance of the study is to define or establish possible environmental agent-induced inflammation of GI epithelial cells. This will give insights into the development of terminal enteritis and inflammatory bowel diseases in humans.